Impulse repeater



Patented Oct. 22, 1940 rarer was IMPULSE REPEATEB Willie Saville,Huyton, Liverpool, England, as-

signor to Associated Telephone 85 -'Ielegraph Company, Chicago, Ill., acorporation of Delaware ' Application June 10, 1938, Serial No. 212,885

- In Great Britain July 5, 1937 3 Claims; (01. 179-16) ductors, relay Dbeing polarised so that super- 15 vision can be effected over thejunction by reversal of current in well-known manner. During each trainof repeatedimpulses these relays are short-circuited. to improve theimpulsing conditions to the'distant exchange equipment, and at 20 theend of each train they are introduced'into the loop circuit of thedistant impulse accepting relay. Due to their high impedance there isthen a momentary drop in the loop current beyond that corresponding totheir ordinary direct our- 25 rent resistance, and unless the impulsingrelay has been energised over a very short junction so that its core iswell saturated, it may release momentarily and give a false impulse toits associated switch.

30 In one method suggested for overcoming this trouble so that thejunction impulsing limits could be extended it was arranged to decreasethe initial impedance of the bridge relays by means of a second windingwhich was short-cir- 35 cuited over their normally closed armatures.This and similar schemes cannot however be easily applied to existingimpulse repeating ar-- rangements, and furthermore they require extracontacts and windings on the bridge relays. It 40 is the object of theinvention to provide a simple and cheap arrangement for overcoming theabove mentioned trouble which can be readily applied to existingequipments without the necessity for appreciable modifications thereto.45 According to the invention in an impulse repeater for use intelephone or like systems arranged so that an impedance bridged acrossthe outgoing circuit is shunted during the transmission of a train ofimpulses, at the same time the 50 shunt is removed a'unit of non-linearresistance material connected across the impedance serves to absorb theinductive kick otherwise produced. By the term non-linear resistancematerial is meant material the resistance of which is sub- 55 stantiallythe same for both directions of current flow but which decreases withincrease of voltage.

The invention will be better understood from the following descriptionof one method of carrying it into effect, reference being had to theaccompanying drawing. This shows a circuit dia- 5 gram of an outgoingimpulse repeater AR of wellknown type which is connected by way of ajunction J to a final selector FS at a distant exchange. It will beunderstood that the diagram shows only suflicient detail to enable theinventicn to be properly understood.

Considering the general circuit operations, when the repeater is takeninto use, relays A and B operate, and incoming trains of impulsessubsequently received are repeated by the armature a2 to the distantimpulse accepting relay lA. Relay 0 holds operated during each train andat armature cl short-circuits relays D and I to improve the impulserepeating conditions.

At the end of each train, relay C releases after its slow period and atarmature cl removes the short-circuit from relays D and I and the unitof non-linear resistance material NLR thereby introducing them into theloop circuit including relay lA. The transient conditions which nowobtain are difficult to describe with any degree of precision but it maybe said broadly that a back E. M. F. of considerable value is generatedin the highly inductive windings of relay IA due to the fall of the loopcurrent and this E. M. F. causes a rapid drop to occur in the resistanceof the material NLR. As the voltage applied across this materialdecreases so will its resistance increasebut during this time theinitial impedance of the bridge relays gradually falls towards the D. C.resistance value. As a result the loop current is prevented from fallingas far as it otherwise would do Without the provision of the non-linearresistance shunt path and relay IA is thereby en-' abled to remainoperated even when long junc- 40 tion lines are in use. When steadyconditions are reestablished, the voltage applied to the material willbe small and will only be equal to the voltage drop across the D and Irelays so that its resistance will be of high value and it willtherefore offer a negligible leakage path during any subsequenttransmission of tones or speech currents over the line conductors.

In a preferred form of carrying the invention into effect, thenon-linear resistance material takes the form of silicon carbide mixedwith carbon and/or tungsten or molybdenum which is agglomerated underpressure and subsequently baked, the resulting mass having aresistancecurrent characteristic which is substantially hyperbolic. Theresistance material may be made into various shapes, for instance, itmay be made in the form of a disc or Washer and the surfacemetal-sprayed at appropriate points as described in my United Statesapplication Ser. No. 198,182, filed March 26, 1938.

I claim:

1. In an impulse repeater, an incoming and an outgoing line, animpedance bridged across the outgoing line, a non-linear resistanceconnected in shunt with said impedance, means responsive to impulsesreceived over the incoming line for transmitting impulses over theoutgoing line, and means effective to short-circuit said impedance onlyduring the transmission of impulses.

2. In combination, a series circuit including a source of current, arelay, and a short-circuited impedance, said relay operated in saidcircuit, means for disconnecting the short circuit from said impedance,and a non-linear resistance permanently connected in shunt with saidimpedance to prevent the relay from being restored by the disconnectionof said short circuit.

3. In combination, a series circuit including a source of current, arelay, and a short-circuited impedance, said relay operated in saidcircuit, means for disconnecting the short circuit'from said impedance,a resistor permanently bridging said impedance and having a resistancevalue controlled by the voltage across said impedance, said resistorhaving, upon the disconnection of said short circuit, a low resistancedue to the back electromotive force generated in the impedance andeffective to increase in resistance as the current flow through theimpedance increases to a steady value, said resistor thereby assistingin maintaining said relay operated during the transient conditionsfollowing the disconnection of said short circuit and comprisingsubstantially an insulator when the flow of current through theimpedance becomes steady.

WILLIE SAVILLE.

